SAT Question 4ddfa209: Area and Volume answer and explanation with Desmos solution

Choice C is correct. The perimeter of a triangle is the sum of the lengths of the three sides of the triangle. It's given that the length of one side of an equilateral triangle is $28$ inches. Since the lengths of the three sides of an equilateral triangle are equal, it follows that the perimeter, in inches, of this equilateral triangle is $28+28+28$, or $84$.